Up-wind type wind turbine generators have a rotor head, which includes a nacelle mounted on a tower and blades attached thereto, and a generator driven by shaft output power of the rotor head. In the wind turbine generators having such a configuration, the blades receive wind power, and the blades and the rotor head are rotated, which is transmitted to the generator. Thus, using the shaft output power obtained by converting wind power to rotary power as the driving source of the generator, power generation using wind power as the motive power of the generator can be performed.
In the wind turbine generators of this type, the generator output power varies depending on the wind speed and the wind direction. Therefore, U.S. Pat. No. 6,320,272 (PTL 1) discloses a technique in which a laser anemometer is used to estimate the wind speed to ascertain the power generating performance of the wind turbine generator.
Furthermore, in the wind turbine generators of this type, in order to utilize the wind energy as much as possible, an anemoscope is mounted on the top of the nacelle so that yaw control is performed such that the nacelle faces into the main wind direction detected by this anemoscope.
However, because the anemoscope is mounted on the top of the nacelle, that is, behind the blades, the anemoscope is located downstream of the blades in the wind direction. Thus, the rotation of the blades changes the wind direction, causing a deviation between the main wind direction detected by the anemoscope and an actual direction of main wind blowing against the blades. As a result, the wind turbine generator generates power when it is deviated with the actual main wind direction. Since the rotational energy given by the wind decreases as the deviation with the wind direction increases, there is a problem in that the generator output power of the wind turbine generator decreases because of the deviation with the wind direction. Furthermore, there is also a problem in that an unbalanced load is applied to the wind turbine generator because of the deviation with the wind direction.